1. Field of the Invention
This invention relates to a telephone apparatus, and more particularly to a telephone apparatus having an inter communication facility and connected to one or more telephone lines and also to one or more other telephone apparatus through one or more extension lines.
2. Description of the Prior Art
Generally, in a system in which a plurality of telephone apparatus (hereinafter, often referred to as merely "telephones") are connected to one or more telephone lines, the transfer of a line connected to one of the telephones to another of them is conducted in either of the following two ways.
When telephones are connected in parallel to a telephone line and an extension line as shown in FIG. 4, the operator presses a hold key to put the telephone line on hold, and informs the person who should receive the call by using the all call paging facility or by word of mouth, and then the person receiving the call takes the handset of his telephone (i.e., offhook) and presses the key corresponding to the line on hold to connect the telephone line to his telephone.
When a PBX 51 or a central control apparatus such as a key telephone 61 having the inter communication facility is provided (as shown in FIGS. 5 and 6), the operator presses a hold key of his telephone to put the telephone line on hold, and then presses one of extension call keys which corresponds to the telephone of the person who should receive the call. The person picks up the handset of his telephone, and then can talk on the transferred line.
In a system in which a central control apparatus is not provided, it is cumbersome to conduct the transfer operation. In order to facilitate the transfer operation, however, it is required to provide a central control apparatus such as a key telephone 61 which is rather expensive.